Rotary pumps



Dec. 13, 1966 B. H.WERRA 3,291,059

ROTARY PUMPS Fil'ed June 8, 1964 jig mj INVENTOR BRUNO H.WERRA ATTORNEYS United States Patent 3,291,059 ROTARY PUMPS Bruno H. Werra, Kenosha, Wis., assignor to Ladish Co., Cudahy, Wis., a corporation of Wisconsin Filed June 8, 1964, Ser. No. 373,153 4 Claims. (Cl. 103-126) This invention relates to improvements in rotary pumps, and more particularly to an improved sanitary pump for liquid foodstuffs, and the like.

Positive displacement pumps of the type herein concerned are widely used in the food-processing industries for pumping milk and other liquid or semi-solid foodstuffs, and are also employed in the chemical and other industries, In order to meet sanitary requirements in the food industries said pumps must be formed of a material which will not contaminate the product. In addition, such pumps are desirably designed with the impellers freely slidably mounted on their shafts so that when the casing cover is removed the impellers can be readily slipped off of said shafts and removed for cleaning. Heretofore, rotary pumps employed in the food and chemical industries have been usually formed of stainless steel, the latter being durable and substantially chemically inert so as not to contaminate the product. However, the physical characteristics of such stainless steel results in rapid wear or galling of the close-fitting, frictionally-engaging parts, particularly in pumps having free-sliding or so-called floating impellers. This wear results in leakage and loss of efficiency, as Well as in shortening the operating life of the pump.

In order to overcome the objectionable galling action in conventional stainless steel sanitary pumps it has been necessary to carefully locate and by a suitable locking-inplace arrangement prevent the two materials which might gall when in contact from touching each other, or low friction plastic inserts or gaskets have in the past been used between the impeller and the pump casing, but such devices are not entirely satisfactory for their intended purposes, and the multiple interfitting pieces and special casing and impeller design which is required adds substan tially to the construction cost of the pump. It has also been attempted to employ a plastic coated impeller, but this construction also requires a special, expensive pump design, and wear occurs relatively soon on the impeller because the plastic coating thereon is not as wear-resistant as metal. Another disadvantage of such plastic materials is that they have a coefiicient of expansion which is quite different from stainless steel, making it impossible to use as close tolerances between the moving parts of the pump as is desirable, as it is necessary to allow for expansion and contraction.

With the above considerations in mind, the principal objects of the present invention are to provide a rotary pump formed of an unusual combination'of materials, wherein the pump casing is stainless steel and the impeller is formed of a special wear-resistant, low-friction metal alloy which is adapted to coact with a conventional stainless steel casing without galling, and which alloy is substantially chemically inert and does not have a deleterious effect on the liquid foodstuff or other product being pumped.

Another object of the invention is to provide a rotary pump formed of a novel combination of materials including a one-piece metal impeller of a durable, low-friction alloy, which alloy also has a very low coefficient of expansion, thus making it unnecessary to allow for expansion and contraction and permitting close tolerances between the relatively movable parts.

A further object of the present invention is to provide an improved rotary pump having an impeller formed of a special low-friction metal alloy, which impeller can be used in a conventional stainless steel casing without galling and without contaminating the product, as described, and which pump is so designed that it can be quickly and easily disassembled for periodic and thorough cleaning.

With the above and other objects in view, which other objects and advantages will become apparent hereinafter, the invention consists of the improved rotary pump disclosed in the following specification, and all equivalents or modifications thereof as may come within the spirit of said invention and within the scope of the appended claims.

In the accompanying drawing, illustrating a preferred embodiment of the invention, and wherein the same reference numerals designate the same parts in both of the views:

FIG. 1 is a front elevational view of the improved rotary pump with a part of the casing broken away to show a portion of the impeller mounting and drive assembly; and

FIG. 2 is an exploded perspective view of the improved pump.

Referring now more particularly to FIG. 1 of the drawing, the illustrated pump assembly includes a bearing and gear housing 10 having a cover 11 through which a rotatable drive shaft 12 is journaled, said drive shaft being operatively connected to a suitable motor (not shown), and there being conventional shaft seals and rings 13 and 14. Mounted on said drive shaft 12 within the housing 10 is a timing gear 15 which meshes with and drives a gear (not shown) on a driven shaft 16 (FIG. 2) mounted below and parallel to said drive shaft. Ball bearing sets 17 and 18 are mounted within the housing within which said drive shaft is journaled. The forward ends of said shafts 12 and 16 project beyond said bearing housing and are provided with spline 12 and 16, respectively, as best appears in FIG. 2.

In the illustrated form of the invention the impellers are of the four lobe type, there being an impeller 37 mounted on the drive shaft 12 and a second impeller 39 (FIG. 2) mounted on the lower shaft 16, said impeller members having meshing lobes and having splined bores 38 and 40, respectively, adapted to slidably, non-rotatably fit on the splined outer end portions of said shafts. While said shafts must be firmly fixed against axial displacement, it is advantageous to have the impeller members slidable thereon, rather than mounted in fixed relation, so that said impellers can be readily slipped off of their shafts when it is desired to thoroughly clean the pump. This is particularly important in the food processing industries, where frequent cleaning is required.

Unlike the impellers in conventional rotary pumps designed for use in the food industries, the impellers 37 and 39 in the present invention are not formed of stainless steel. Instead, it is a feature of the present invention to provide for use with a stainless steel casing, impellers of an alloy consisting of from 13.7-14.4 parts aluminum, 4.05.25 parts iron, 0.50 maximum of unknown impurities, and the balance copper. A pump constructed as above described and including impellers of this unusual copper-base alloy has certain unexpected advantages over conventional pumps having stainless steel impellers, as well as casings, as will be hereinafter described in greater detail. Each impeller is formed of onepiece construction, including the hub, from the alloy.

Mounted on the forward end of the bearing housing 10, and in covering relation to said impellers 37 and 39 is an impeller casing 25 having a back wall 26, and a removable front plate or cover 42, there being an O-type sealing ring 44 mounted in the inner face of said cover to prevent leakage. The back wall 26 is provided with openings 27 for the impeller shafts 12 and 16, and a plurality of resilient, coacting sealing rings 23 function to provide a leakproof shaft bearing. In the illustrated embodiment of the invention, four spaced, threaded studs 21 project forwardly from the housing 10 and are projected through bores 24 (FIG. 2) spaced around the periphery of said impeller casing 25, and through aligned apertures 43 in said front cover. Retaining nuts 22 are threaded onto the outer ends of said studs to removably secure said cover 42, casing 25, and housing 10 together, said nuts 22 being readily removable to permit the detachment and removal of said cover and casing members, and the withdrawal of the floating impeller members 37 and 39, for thorough cleaning.

The impeller casing 25 and front cover 42 in the present invention are preferably formed of stainless steel, and as best appears in FIG. 2, said casing is provided with an interior cavity including a pair of communicating, generally-circular chambers 28 and 29 within which the impellers 37 and 39 snugly fit for rotation, respectively. Communicating with the casing cavity is a suction port 32 and a discharge port 34, and fittings 33 and 35 project outwardly therefrom for coupling the pump to suitable lines (not shown).

In operation of the illustrated pump, liquid sucked into the impeller casing through the suction port 32 is forcibly discharged through the discharge fitting 35. In order to maintain pumping efiiciency it is important that the side faces 37, 37", 39' and 39" of said axially slidably mounted impellers 37 and 39 be closely positioned adjacent the inner surfaces of the rear wall 26 of the impeller casing and with the cover 42, in order to prevent leakage across the end faces of said impellers.

Because of the close fit between the side faces 37', 37", 39 and 39" of the slidable impeller members 37 and 39 and the adjacent casing surfaces there is frictional contact therebetween during operation. With conventional sanitary pumps wherein both the impeller and easing are formed of stainless steel, there is galling and rapid wear on said members. As hereinabove mentioned, in order to eliminate this shortcoming, attempts have been made in the past to mount Teflon or other low-friction gaskets or seals between said relatively movable members, or to coat the impeller with plastic, but such devices have not proven entirely satisfactory and the special casing and impeller design required therefor adds substantially to the manufacturing cost of the pumps. The alloy utilized in the present impellers has a high Rockwell C hardness and is durable and long-lasting, thus greatly increasing the operating life and efficiency of the pump. Moreover, said alloy is substantially chemically inert, and does not have a deleterious effect on the liquid foodstuff or other material being pumped. The impellers of the present invention have the following physical properties:

Minimum Average Tensile Strength 75, 000 85, 000 Yield Strength.-. 60, 000 70, 000 Elongation O. 0. Reduction of Area"-.. 0. 0 0. 0 Brinell 311 331 Rockwell0 (By Conversion) 32 35 ocfileient of Ex )ansion Inches er inch per C F. (100009 Wt. per Cubic Inch. 2571 Thennal Conductiv y, c s 16 Specific Gravity... 4. 12 Modulus of Elasticit 13,960,000 Elastic Limit of Co1npressi0n, p.s.i 65, 000 Ultimate 01' Compression, p.s.1 171, 000 Shear Stress, p.s.i 60, 000-70, 000 Charpy, ft. lbs 2 Izod, ft. lbs 2 The impeller of the present invention is a success, whereas an all-copper impeller would be unsatisfactory for dairy and food use because it has an objectionable reaction With milk and other edible products, affecting the amount of Vitamin C therein, and is likely to show up objectionably in tests of the product. With the copperbase alloy utilized herein, however, the low friction properties of the copper are maintained while the aluminum content in said alloy functions to tie up the copper and prevents the copper from having its usual chemical reaction with milk or the like. Furthermore, there is no contamination of the product.

A further important advantage of the present invention is that the special copper base alloy employed in the manufacture of the impeller has a very low coefficient of expansion. The result is that with the present invention it is unnecessary to allow tolerances for contraction and expansion of the metal, and close fits are possible between the relatively movable members, thereby promoting the operating efficiency of the pump.

From the foregoing detailed description it will be seen that the present invention provides a novel rotary pump for liquid foodstuffs, and the like, which is a definite improvement in the art. It is to be understood that while the present pump is intended for use primarily in the food processing industries it has utility in the chemical or other industries as Well. Moreover, while a preferred form of positive displacement pump has been illustrated and described, the invention is not to be confined to the particular pump structure shown. It is contemplated that various changes or modifications will occur to those skilled in the art, and it is intended to cover not only the illustrated embodiment of the invention, but also any and all modifications or variations thereof as may come within the spirit of the invention, and within the scope of the following claims.

What I claim is:

1. In a positive displacement pump having a stainless steel casing with opposite side walls and having spaced parallel impeller shafts, the improvement comprising an all metal impeller axially slidably mounted on each shaft and having end faces in close-fitting rotatable engagement with the stainless steel of said side walls of the pump casing, each impeller being of one-piece construction and formed of a copper base alloy containing 13.7-14.4 percent aluminum, 4.0-5.25 percent iron, and the balance substantially all copper, whereby an all-metal floating impeller construction may be used in a stainless steel casing with a minimum of galling action and with no deleterious effect on food material such as milk.

2. In a sanitary pump having a stainless steel casing with opposite end walls and having an impeller shaft, the improvement comprising an impeller axially slidably mounted on said shaft and having end faces in close-fitting rotatable engagement with the stainless steel side walls of the pump casing, said impeller being of onepiece construction and formed of a copper base alloy containing 13.7-14.4 percent aluminum, 4.0-5.25 percent iron, and the balance substantially all copper, whereby an all-metal floating impeller construction may be used in a stainless steel casing with a minimum of galling action and with no deleterious effect on food material such as milk.

3. A positive displacement pump comprising a pair of closely-interfitting lobed impellers, the axes of rotation of said impellers being spaced and fixed relative to each other, a stainless steel pump casing for said impellers having a suction opening and a discharge opening, the inner surface of the stainless steel side walls of said casing being parallel to and closely adjacent the end faces of said impellers, a first shaft for one of said impellers journaled in said casing, said impeller being axially slidably mounted on said first shaft and having splined engagement therewith a second shaft for the other of said impellers journaled in said casing, said last impeller being axially slidably mounted on said second shaft, and means fixedly supporting said shaft against axial movement, said impellers being formed of a copper base alloy containing approximately 13.7-14.4 percent aluminum, 4.05.25 percent iron, with the balance substantially all copper, whereby an all-metal floating impeller construction may be used in a stainless steel casing with a minimum of galling action and no deleterious effect on food material.

4. A positive displacement pump comprising a pair of closely-interfitting lobed impellers, the axes of rotation of said impellers being spaced and fixed relative to each other, a stainless steel pump casing for said impellers having a suction opening and a discharge opening, the inner surface of the stainless steel side walls of said casing being parallel to and closely adjacent the end faces of said impellers, a first shaft for one of said impellers journaled in said casing, said impeller being axially slidably mounted on said first shaft and having splined engagement therewith, a second shaft for the other of said impellers journaled in said casing, said last impeller being axially slidably mounted on said second shaft, and means fixedly supporting said shafts against axial movement, said impellers being formed of a copper base alloy containing a small amount of iron and a sufiicient amount of aluminum to tie up the copper and prevent it from reacting with food material such as milk, said alloy providing for a minimum of galling action against stainless steel and having a low coeflicient of expansion.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Section 140, Nov. 1, 1954, Myers Pump Bulletin (Revised Feb. 15, 1957), (pages 1-5, 5 pages).

MARK NEWMAN, Primary Examiner.

WILBUR J. GOODLIN, Examiner. 

1. IN A POSITIVE DISPLACEMENT PUMP HAVING A STAINLESS STEEL CASING WITH OPPOSITE SIDE WALLS AND HAVING SPACED PARALLEL IMPELLER SHAFTS, THE IMPROVEMENT COMPRISING AN ALL METAL IMPELLER AXIALLY SLIDABLY MOUNTED ON EACH SHAFT AND HAVING END FACES IN CLOSE-FITTING ROTATABLE ENGAGEMENT WITH THE STAINLESS STEEL OF SAID SIDE WALLS OF THE PUMP CASING, EACH IMPELLER BEING OF ONE-PIECE CONSTRUCTION AND FORMED OF A COPPER BASE ALLOY CONTAINING 13.7-14.4 PERCENT ALUMINUM, 4.0-5.25 PERCENT IRON, AND THE BALANCE SUBSTANTIALLY ALL COPPER, WHEREBY AN ALL-METAL FLOATING IMPELLER CONSTRUCTION MAY BE USED IN A STAINLESS STEEL CASING WITH A MINIMUM OF GALLING ACTION AND WITH NO DELETERIOUS EFFECT ON FOOD MATERIAL SUCH AS MILK. 